The subject matter disclosed herein relates generally to seal assemblies between rotating and stationary components of machines and, more particularly, to seal teeth mating surfaces for receiving seal teeth in a turbine during different phases of turbine operation.
As used throughout this application, reference to machine is to include machines having rotating and stationary components, including, for example, a steam turbine, a gas turbine or a compressor.
In a machine, a seal assembly between rotating and stationary components is an important part of machine performance. A seal assembly may be comprised of a seal tooth and a mating surface. For example, in a steam turbine, it will be appreciated that the greater the number and magnitude of steam leakage paths, the greater the losses of efficiency of the steam turbine. In a main flow path of a steam turbine, a plurality of stages are used to efficiently extract energy from the high-pressure and high-temperature fluid flow to drive an electrical generator. In each stage, there is a row of stationary blades (nozzles) and a row of rotating blades (buckets). Clearances are needed between the nozzles and a rotor and between the buckets and a casing. Improving the seal assemblies and reducing steam leakage paths improves steam turbine efficiency.
FIG. 1 shows a partial side cross-sectional view of a known machine 100. In machine 100, a rotor 102 is surrounded by a casing 104. Rotor 102 is attached to a thrust bearing 103 (shown schematically). Rotating components 107 of machine 100 may be include rotor 102 and radially extending rotating components 106. Stationary components 109 may include casing 104 and radially extending stationary components 108. Casing 104 and rotor 102 may have different thermal properties. For example, casing 104 and rotor 102 may have different thermal masses. Differing thermal masses may be due to differing relative sizes or composition of differing materials.
For example, in a steam turbine, the thermal mass of rotor 102 is relatively small compared with that of casing 104. Prior to start up, the rotor 102 and casing 104 are in a cold assembly position. During a shut-down or temperature increasing of steam turbine, rotor 102 heats up and expands faster than casing 104. As a result, rotor 102 changes position relative to casing 104. For example, rotor 102 moves in an axial direction away 110 from thrust bearing 103 relative to casing 104. As casing 104 and rotor 102 approach a same temperature, rotor 102 returns to approximately its cold assembly position relative to casing 104 until the parts reach the same temperature, at which point steam turbine reaches a steady-state. In steady-state, relative position of rotor 102 to casing 104 remains substantially the same if the rotor and casing are made of the same materials or materials with similar thermal expansion rates. During a shut-down or temperature decreasing of steam turbine, rotor 102 cools faster than casing 104 and rotor 102 changes position relative to casing 104 in the opposite direction as during shut-down or temperature increasing. For example, rotor 102 moves in an axial direction towards 112 thrust bearing 103 relative to casing 104. In addition to axial movement, rotor 102 may move in a radial direction 114 due to vibration during shut-down or temperature increasing and shut-down or temperature decreasing or temperature decreasing. A person skilled in the art will readily recognize that in a machine 100 the relative movement of rotor 102 to casing 104 will depend upon the differing thermal properties. For example, if rotor 102 is relatively large in thermal mass compared to casing 104, rotor 102 would heat slower than casing 104 during shut-down or temperature increasing.
Seal teeth 116 may be placed on rotor 102, radially extending rotating components 106, casing 104, or radially extending stationary components 108. FIG. 2 shows a partial side cross sectional view of a known machine 100 including a radially extending rotating component 106, seal tooth 116, casing 104, and seal tooth mating surface 122. Seal tooth 116 may be received by a seal tooth mating surface 122 on casing 104, rotor 102, radially extending rotating component 106, or radially extending stationary component 108 depending upon seal tooth 116 placement. A seal assembly 123 is comprised of seal tooth 116 and seal tooth mating surface 122. Seal assembly 123 may include HiLo, interlocking, and straight-through configurations. During shut-down or temperature increasing or shut-down or temperature decreasing, seal tooth 116 may contact seal tooth mating surface 122 causing damage to seal tooth 116, to seal tooth mating surface 122, or both seal tooth 116 and seal tooth mating surface 122. Wearing of seal tooth 116, seal tooth mating surface 122, or both seal tooth 116 and seal tooth mating surface 122 may cause leakage increase particularly upon reaching steady-state operation.
Seal tooth 116 may include a brush seal. During shut-down or temperature increasing or shut-down or temperature decreasing, the tip of brush seal may have too much interference with seal tooth mating surface causing the brush seal tip to wear. Wearing of brush seal tip may cause more leakage particularly upon reaching steady-state operation.